In formulating a paint composition, it is the general practice to disperse pigment in a part of a resin which constitutes the main ingredient of a resinous vehicle of the final paint, and the thus obtained colored base composition is then diluted with the remaining amounts of said resin, together with other optional resins, and diluent(s). However, in these days, since the user's requirements are diversified, there is a trend that to manufacture various grades of paints limited quantities.
The pigments used in the paint area are lacking in uniformity in their surface properties, and therefore, a different dispersing resin has to be used for the respective kinds of pigments and thus there is a problem on reducing the cost of producing the composition on a mass production basis. If it is possible to provide beforehand for reserve stocks of various colored base compositions with a common resinous vehicle, each in larger quantities, and to formulate the desired paint composition by using said stock or combination of stocks and diluting with said or other resin(s) and solvent(s) as the occasion calls, inestimable benefits would be attained in the paint production. However, very unfortunately, such a multi-purpose dispersing resin has not yet been found.
An object of the present invention is, therefore, to provide a multi-purpose dispersing resin having an excellent affinity in acids and bases and to the respective pigment and resin to be used. That is good affinity and hence excellent dispersion may be obtained with the combination of pigment and resin each having the opposing property. The inventors, paying due attention to this S.phi. rensen's interpretation and suspecting that if an amphoteric resin having both acidic and basic characteristics can be obtained from the conventional acidic and basic resins used in the paint compositions, it must be possesed of good compatibility with various resinous vehicles and excellent dispersing ability toward various pigments having each different surface properties. The present invention has been achieved as a result of various studies made on various bonding systems between acidic resins and basic resins, suitability and their as dispersing resin.